High-resolution repair of photomasks using a deep-UV-laser-based defect repair system

A laser-based defect repair system developed at Excel/Quantronix is designed to repair photomasks with submicron resolution. The laser of the repair unit consists of a gain-switched Ti:Sapphire system configured to operate at 248 nm. The deep-UV light is obtained by frequency tripling the fundamental Ti:Sapphire wavelength. The Ti:Sapphire laser system generates pulses with temporal duration of approximately 12 ns and pulse energies up to approximately equals 50 (mu) J at repetition rates from single-shot to 500 Hz. This solid-state laser system provides good pulse-to-pulse stability and excellent beam quality, features that are necessary for high resolution repairs. The repair unit is based on a state-of-the-art air-bearing positioning system with +/- 15 nm in-position stability. The accompanying optical system is designed to include a high-resolution microscope providing transmitted light illumination (248 nm and 365 nm) and reflected light illumination. A series of CCD cameras provide high resolution viewing at various magnifications. The system capabilities include submicron repair of both clear and opaque defects in an open-air environment by laser ablation and laser-assisted photolytic deposition. The optical system for laser processing and delivery is designed for diffraction-limited performance. Clear and opaque repair results performed on binary photomasks are presented.